This invention relates to tubeless pneumatic tires. More specifically, it relates to an innerliner (hereinafter innerliner, or liner, or liner ply) which is the inner-most layer of the tire structure for maintaining the internal air pressure in such a tire.
U.S. Pat. No. 5,484,005, to Morehart et al, assigned to the assignee of the present application, displays the use of graft copolymers of diene monomers and copolymers and metal salts of an unsaturated carboxylic acid to form rubber skins in pneumatic tires having resistance to air permeability. This patent does not recognize the ability of metal salts of the unsaturated carboxylic acid to be grafted onto non-diene type rubbers to increase resistance to air permeability.
In a typical pneumatic tire manufacturing operation several plies of reinforced rubber were laid up during the tire building step and these became permanently laminated during the molding and curing step. Rubber innerliners are utilized in tubeless pneumatic tires because of their high resistance to air permeability. The innerliner is not wrapped around the bead cores but extends from bead to bead covering only the inner periphery of the tire. This is consistent with its basic function which is to prevent permeability of air through other tire components such as body plies, sidewalls, etc. Conventional rubber innerliners are generally composed of highly saturated rubbers such as butyl rubber, halogenated butyl rubbers or blends of butyl rubbers with small amounts (e.g. 10% by weight or less) of natural rubber because butyl and halobutyl rubbers represent the best air barrier among elastomers. In order to give a satisfactory performance in air pressure retention, the thickness of a butyl rubber based innerliner in a good quality auto tire must be on the order of about 60 mils.
When a vehicle is running, all of the components in the tires are flexing at a high frequency. A certain amount of energy is consumed as a "loss" due to hysteresis, which is the major contributor to the rolling resistance of the tire and is indicated by the rise in the temperature of the material. A need exists in the tire industry for a reduction in the mass of any one or more components of the tire, without impairing the performance of the intended function of the component(s), that would reduce its share of the energy loss and result in an improvement of tire performance and fuel economy.
The rolling resistance of a tire can also be improved by increasing the air pressure in the tire. However, with the butyl or halobutyl rubber innerliner, the higher pressure can only be maintained by a thicker and heavier liner. The added weight of a thicker innerliner would offset the gain from the higher air pressure because it would increase the hysteresis loss. Therefore, the only meaningful way to achieve a higher tire pressure would be by improving the air barrier property of the innerliner. The present invention solves the above mentioned problems of the tire industry.
The use of such rubber innerliners in tubeless tires while beneficial in preventing air permeability presents a number of significant disadvantages because the use of a separate rubber innerliner adds approximately 1.5 pounds to the total weight of the tire.
Accordingly, it is desireable to reduce gas transmission through the innerliner used in tubeless tires thereby allowing thinner interliners to be used and reducing the total tire weight.